Subcomponents of hormone-sensitive adenylate cyclase have been identified by determination of requirements for reconstitution of hormone-dependent enzymatic activity in membranes of cultured cells that are deficient in various steps of the pathway. A catalytic protein, a regulatory protein, hormone receptors, and a hypothetical factor whose deficiency explains the phenotype of the uncoupled (UNC) S49 cell are under study. These proteins are to be characterized and their mechanisms of interaction are to be studied.